Body construction design is always problematic in regions where two different metals are joined, in particular, regions where galvanic corrosion is likely to occur. Galvanic corrosion can occur if a large thermodynamic potential difference exists between two metals, for example, between aluminum and steel. Many steel coatings have been developed over the years to lower the thermodynamic driving force when aluminum is in contact with steel, such as aluminized coatings, hot dipped galvanized, or electro galvanized. The zinc or aluminum coatings effectively seal off the steel surface and lower the galvanic difference, as zinc or aluminum coatings are closer in thermodynamic potential to aluminum than steel. These coatings are applied at the rolling mill and coat the top and bottom surfaces of the steel.
However, during subsequent processing, where the steel rolls are cut and blanked into specific shapes prior to stamping, the resulting bare exposed edges of the steel blanks are not protected by these coatings. Once these blanks are formed into usable structures and components and placed into service, where they may be exposed to the elements, the uncoated and bare exposed edges of the steel structures and components are vulnerable to attack by electrolytes, such as salt and water, particularly where the steel structures and components are mounted to aluminum structures. Hence, a solution that addresses these concerns would be advantageous.
The solution disclosed herein is a geometric and mechanical separation between the aluminum and the bare exposed edges of the steel structures of the tubes/stampings. In particular, a joint is disclosed that comprises an aluminum member attached to a steel member having an adjoining portion in substantially juxtaposed abutting relation with the aluminum member, the steel member having a ramp portion terminating in a bare exposed edge, the ramp portion being displaced from the aluminum member to form a gap between the aluminum member and the bare exposed edge to prevent corrosion of the bare exposed edge without the use of adhesives and sealants.
Thus, the solution presented by the present joint for a motor vehicle body is a relatively low-cost, light-weight structure that protects the respective aluminum and steel components from corrosion.